The background and main objects of the invention may perhaps best be understood by taking a typical automotive piston type internal combustion engine and modifying same hypothetically to obtain greater theoretical efficiency. Automotive engines are used with frequently varying power output for obvious reason, with the power output varied by admitting a varying weight of combustible gas charge to the combustion chamber. This is achieved by choking of or throttling, the gas charge intake. Let us assume that 75% of the usage time, automotive engines typically are used at 50% throttle. To improve the overall efficiency the intent is to obtain greater efficiency at this 50% throttle setting, since this 50% throttle setting represents by far the greatest usage factor.
First of all, the constant stroke of the typical engine is too long for the required intake of 50% gas charge weight; this wastes motion, and energy in the way of excessive friction, lost time and pumping losses, with the piston stroking longer than necessary against a vacuum. Secondly, the required 50% gas charge weight is not compressed to maximum permissible value. It is well known that for efficiency the gas charge must be compressed to maximum permissible value. Since the geometric compression ratio is fixed and determined by the gas compression ratio of 100% gas charge weight intake, the 50% intake is compressed to a volume which is roughtly 50% of the maximum permissible. So the first two hypothetical improvements to be made to the typical engine, are to provide an engine wherein the intake and compression strokes are reduced in length to 50%, while the power stroke is maintained at 100% length, and to raise the geometric compression ratio to the maximum permissible value for the new 50% gas charge weight intake, or roughly reduce the geometric volume of the combustion chamber at the end of compression stroke to 50% of the original volume. We have lost the original maximum power output potential of the hypothetical engine, but we have recuperated a substantial amount of this loss by less friction losses, less pumping losses, less wasted time, since the intake and compression stroke take only half as long, allowing more time for the expansion and exhaust strokes, and by fully compressing the 50% gas charge weight intake to maximum permissible value. The original engine, again having a fixed stroke length, probably did not expand the burning gas charge to full potential, even at 50% throttle setting, so we will improve on this by giving our hypothetical engine also an optimum expansion stroke. To overcome the problem of loss of maximum power output, we will introduce extra gearing in the transmission of our vehicle and our hypothetical engine will require a throttle setting on the average much closer to wide open.
The next hypothetical improvement to be made, is to drastically improve the usage factor for the highly stressed components of the engine.
It is known that for overall efficiency in positive displacement, piston type internal combustion engines, every aspect of engine operation, every function and every component must be optimized. Piston type engines utilize a cyclic combustion process and cyclic processes tend to have a weight penalty and power output penalty, since cyclic processes pass through a short duration power pulse followed by a re-charging cycle. The short duration power pulse places high peaking stresses on the components, making them relatively heavy, while the time wasted as required for re-charging is not conducive to high specific power output. Continuous combustion process engines, such as jet engines and rockets, therefore achieve uniform, continuous stressing of components, rather than short duration peak stressing, achieving lighter construction, while the continuous process, without cyclic stopping of the power output for cyclic re-charging, results in very high specific power outputs. In all transportation vehicles, the emphasis on weight reduction is becoming more important as the cost of fuels rises. Therefore, it is important to divorce light duty functions from components which are made to withstand heavy stresses. In conventional piston type engines, the complete combustion chamber, the valving means, and the power output components, the piston, connecting rod, crankshaft etc. are designed to withstand the peak combustion stresses, and it is inefficient to use these heavy duty components for light duty functions. In conventional four cycle engines, only the power output stroke utilizes the strength of the components, and eighty percent of the total time of operation is utilized for scavenging and re-charging the combustion chamber, to the time of ignition. Super charging these engines only increases the peak stresses and does not significantly alter the efficiency. Turbocharging eliminates the pumping losses of the piston whiel re-charging, and results in a much greater gas charge taken in, while also resulting in the piston delivering a little power during the intake stroke, as the gas charge is forced under pressure into the cylinder. These "boost" pressures are from five to thirty pounds per square inch, and the overall result of turbocharging therefore is an increase in efficiency, as well as an increase in specific output, the latter again, mainly at the cost of higher stressed components. The piston compression ratio is lowered but the overall compression ratio is approximately identical for these engines. Compound turbocharging, whereby some of the power output of the exhaust driven turbocharger is delivered to the crankshaft, is more efficient yet, but it is not practical for automotive use, since the high rotational inertia of the turbine is not readily switched on and off, to follow the continuously changing power demands of automotive engines. Raising the compression ratio extracts more energy from the fixed available energy in the gas charge, with some of the known reasons being: the closer proximity and higher agitation of oxygen molecules and fuel molecules resulting in stronger combustion; this stronger combustion acting in a smaller volume, resulting in higher pressures on the piston over its complete power stroke. In a typical engine, it is known that raising the compression ratio from 10.75 to 14.8 overall can raise the fuel economy by eight percent; but detonation becomes a serious problem at these higher ratios.
None of the measures so far discussed improve the utilization factor for the basic component parts involved. To achieve higher specific output, in two cycle engines, the exhaust stroke and the intake stroke are eliminated from the combustion chamber. The spent gases are spilled out of ports or valves at the bottom position of the piston, or forced out by pressurized air. Air or air and fuel is admitted to the combustion chamber while the piston is still generally in the bottom position, and the subsequent upstroke of the piston compresses this gas charge to the required value. Spent exhaust gasses are not positively and entirely removed, especially in smaller engines which depend on the dynamic, resonant characteristics of the expanding spent gas charge for scavenging, and some of the incoming fresh gas charge is lost with the exhausting spent gasses. Conventional four cycle engines are better in this respect but still do not usually employ a positive means of expelling all spent gasses either, since the final volume of the combustion chamber with the piston in the top position retains some spent gasses. Here also the dynamic resonant characteristics of the spent gas charge can be used to help extract more spent gasses, but again this is effective only over a very limited r.p.m. range. Conventional two cycle engines extract approximately twenty-five percent of the available energy of the fuel, while for conventional four cycle engines this figure becomes approximately thirty-three percent; an eight percent improvement over two cycle engines, indicating the importance of eliminating spent gasses. Exhaust gas remnants in the fresh gas charge deteriorate power and efficiency for two known reasons: many fuel molecules are shielded by exhaust gas molecules and cannot oxidize fully; exhaust gas remnants take up volume and the fresh charge is therefore not reduced in volume, or compressed, to maximum valve. Heat rejection through cooling fins and radiators etc., accounts for approximately thirty-three percent, while the energy lost with the exhaust gasses accounts for approximately the remaining thirty-three percent of the initial available energy. In conventional engines, the constant geometric engine displacements results in excessive pumping losses during average power demands, and if the volumetric displacement is varied by valve timing adjustments during operation, there still remains the wasted motion due to constant stroking of the intake and compression stroke. Adjusting power demand by choking off, or "throttling", the intake, results in significant power losses since it takes considerable energy to maintain a vacuum across a restricted opening. This background illustrates some of the areas wherein efficiency improvements are sought as objects of this invention and these may be summarized, as follows: